* glom/libglom/db_utils.[h|cc]:
	* glom/base_db.[h|cc]: Moved get_fields_for_table(),
	get_fields_for_table_one_field(), get_lookup_fields(), and
	get_lookup_value() to the DbUtils namespace, taking an extra
	Document parameter.
	* glom/libglom/document/document.[h|cc]: Moved get_lookup_fields() to
	DbUtils too.

	* glom/base_db_table_data.cc
	* glom/mode_data/box_data.cc
	* glom/mode_data/box_data_calendar_related.cc
	* glom/mode_data/box_data_details.cc
	* glom/mode_data/box_data_list_related.cc
	* glom/mode_data/db_adddel/db_adddel.cc
	* glom/mode_design/box_db_table_relationships.cc
	* glom/mode_design/fields/box_db_table_definition.cc
	* glom/mode_design/fields/dialog_fielddefinition.cc
	* glom/mode_design/layout/dialog_layout_list_related.cc
	* glom/print_layout/canvas_print_layout.cc: Adapted. This shows how
	often we call this very inefficient function. It would be better to
	just make sure that the document has up-to-date information from the
	database and just use the Document's information.

	* Makefile_tests.am:
	* tests/test_selfhosting_new_then_lookup.cc: Added a new test of
	these functions, including retrieval of a lookup value.